Effective irrigation requires application of the right amount of water at the right time and right location. The use of soil moisture sensors can help producers with irrigation scheduling by providing information about when and how much water to apply.

A wide range of commercial soil moisture sensors are available. Therefore, when selecting a sensor, cost, product support, convenience, soil and crop type, and sensor accuracy are all important factors to consider.

Under optimum conditions, soil water in the crop root zone should be maintained between the field capacity and manageable allowable depletion. Allowing soil water to drop below this level will cause unnecessary stress to the crop.

Field capacity is defined as the point at which all of the gravitational or easily drained water has drained from the soil. For many irrigated soils, this is approximately 1/10 bar of tension. The maximum allowable depletion (MAD) is the maximum amount of plant available water allowed to be removed from the soil before irrigation refill occurs (see below).

The value of MAD (and therefor the irrigation trigger point) varies by crop and soil type. For most landscape purposes, a MAD of 50% represents a suitable overall value. For shallow root systems or heavily compacted soils a smaller allowable depletion should be considered (30-50% MAD).

There are several ways to monitor soil moisture ranging from the traditional feel and appearance method to a variety of commercially available soil moisture monitoring sensors.

Proper installation and placement of the sensors in the crop root zone is critical. Sensors should be installed in locations that best represent overall field conditions. Considering the significant variation in most fields due to soil type, growers will get more representative results by using sensors installed at several locations across a field. Avoid sensor installation where there is a large gap between the plants, or near the edge of the field.

For sugar beets, the recommended depth for soil moisture sensors is at 1, 2, 3, and 4 feet deep. For dry beans or barley, sensors should be installed at 1, 2, and 3 feet deep.

For more information about this and other irrigation topics, contact Vivek Sharma at 307-754-2223 or vsharma@uwyo.edu.